This application is based on an application No. 219834/1999 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a toner for an electrostatic latent image development which may be used in an electrophotography, an electrostatic printing and the like.
2. Description of the Related Art
In the fields of the electrophotography and electrostatic printing, there are problems that inorganic fine particles which are added to toner particles are adhered to a photosensitive member, and black spot (BS) which brings about image defects is occurred in a process of a blade cleaning.
For example, the following prior arts have heretofore been proposed in order to solve these problems.
U.S. Pat. No. 4,883,736 teaches that toner spots can be suppressed by adding internally or externally a higher alcohol whose carbon atom numbers are 30-300, preferably 30-50. Japanese Patent Publication (KOKAI) No. 282096/1994 discloses that it is possible to suppress a comet or a filming of fine powders onto the photosensitive member in the blade cleaning by employing a higher alcohol in the case where an external additive is used within a specified range.
In Japanese Patent Publication No. 72798/1993, a technical idea is exemplified wherein a carboxylic acid having a lower alkyl chain is added to toner particles as a solid lubricant in order to solve the aforementioned problems. However, in fact the technical idea has a problem that a heat resistance of the toner to which the carboxylic acid is externally added becomes worse, and the toner is not fit for a practical use unless the carboxylic acid is converted to a metallic salt in order to increase a melting point of the acid.
According to the aforementioned prior arts, the functions to suppress noises on the photosensitive member may be explained by a technical idea wherein the higher alcohol or higher fatty acid forms a lubricative film on the photosensitive member at the time of cleaning, and the lubricative film suppress the adhesion and filming of the toner components onto the photosensitive member. With respect to the electrophotographic process having the blade cleaning process, it has publicly been known that the adhesion and filming (black spot (BS)) of the inorganic fine powders and other components of the toner can be suppressed by externally adding the higher alcohol or higher fatty acid.
However, as described in any of the aforementioned publications, it has been indicated that there is a problem that a maintenance of heat resistance of the toner cannot be ensured unless carbon atom numbers of the higher alcohol or higher fatty acid employed in these prior arts are 30 and more from the viewpoint of the relationship between the carbon atom numbers and a starting point of a melting of said higher alcohol or higher fatty acid. According to a follow-up test by the inventors of the present application to confirm the effect of the higher alcohol described in the aforesaid publications, it has been confirmed that (i) a large quantity of the higher alcohol is necessary to suppress BS, (ii) an effect of forming the lubricative film is insufficient, and (iii) problems, such as a poor electrification of the toner, a decrease of an environmental stability and the like are newly occurred when a large amount of the higher alcohol is added to the toner particles.
In consideration of the functions of the aforementioned higher alcohol or higher fatty acid, although there is a reason to expect that the higher alcohol or higher fatty acid having lower molecular weight may bring about a higher effect from the viewpoint of the suppression of the adhesion and filming onto the photosensitive member, they cause a lethal problem that the heat resistance of the toner becomes worse. The prior arts could not cope with the problem.
The present invention provides a toner composition which suppresses an occurrence of BS (black spot) which brings about image defects in the process of a blade cleaning, said black spots being caused by an adhesion of inorganic fine particles which are added to the toner particles to the photosensitive member.
The present invention relates to a toner for an electrostatic latent image development which comprises the following aliphatic higher alcohols (1) or higher fatty acid (2) as an external additive:
H"Parenopenst"CH2"Parenclosest"nOH (n: an integer)xe2x80x83xe2x80x83(1)
H"Parenopenst"CH2"Parenclosest"mCOOH (m: an integer)xe2x80x83xe2x80x83(2)
wherein number-average carbon atom numbers of the aliphatic higher alcohol or the higher fatty acid are 21-29, contents of the ingredients having carbon atom numbers of not more than 20 are not more than 2% by weight, and contents of the ingredients having carbon atom numbers of not less than 30 are not more than 2% by weight.
In the investigating course to achieve the present invention, it has been proven that the higher alcohols or the higher fatty acids which have formerly been on the market as a general-purpose product contain large amounts of hydrocarbons having no hydroxyl group or carboxyl group, and that the commercially available products having carbon atom numbers of not less than 30 actually contain not less than 3% by weight of the ingredients whose carbon atom numbers are not more than 20.
The high-purity higher alcohols (e.g., Uniline Alcohol(trademark) (Petroright Co.) and the like) or higher fatty acids (e.g., Unisit(trademark) (Petroright Co.) and the like) which are produced by a different process from a general preparation process have been on the market, and said high-purity products are actually employed in the examples of the aforementioned prior arts. However, as regards these higher alcohols and higher fatty acids, it becomes clear that although contents of the hydrocarbons become little, a molecular weight distribution is broad and few percents of the ingredients whose carbon atom numbers are not more than 20. According to the results of actual differential thermal analyses of these commercially available higher alcohols and higher fatty acids by means of a differential scanning calorimeter (DSC), it has been confirmed that the higher alcohols or fatty acids whose carbon atom numbers are not less than 30 begin to slightly exhibit an endothermic process from around 50xc2x0 C. Therefore it could have easily been predicted that these higher alcohols or fatty acids exert bad influence on the heat resistance of the toner in the case where large amounts of these compounds are added to the toner.
The present inventors have purified the general-purpose aliphatic higher alcohols or higher fatty acids which are on the market in such a way that a purity of single molecular weight of these compounds whose carbon atom numbers are 15-40 becomes not less than 98%, and prepared plural standard samples according to a molecular difference of said purified compounds. A starting temperature of a melting of the single standard sample or homogeneous mixtures thereof was measured by means of DSC. According to the results of these measurements, it could have been confirmed that the starting temperature of the melting (starting temperature of the endothermic process) becomes not less than 55xc2x0 C. provided that a distribution of molecules whose carbon atom numbers are not more than 20 is not more than 2% by weight even if average carbon atom numbers of the higher alcohols or higher fatty acids are not more than 29. From a viewpoint of a maintenance of the heat resistance, the desirable starting temperature of the melting is not less than 55xc2x0 C. If said temperature becomes less than 50xc2x0 C., said maintenance becomes worse, and the higher alcohols or the higher fatty acids could not be used. On the other hand, it has been proven that it is necessary to add large amounts of the high-purity higher alcohols or higher fatty acids having carbon atoms of not less than 30 in order to suppress BS, said higher alcohols or higher fatty acids being regarded as a suitable additive in the prior arts, and that said higher alcohols or higher fatty acids do not necessarily have a suitable molecular weight for the suppression of BS.
Meanwhile it has been found out that the suppression effect of BS becomes insufficient if the higher alcohols or higher fatty acids whose melting points are too high are present.
Judging from the above investigated results, the present inventors conjectured that low-molecular ingredients having carbon atoms of not more than 29 actually contribute to the suppression of BS in the case of the higher alcohols or higher fatty acids having average carbon atom numbers of not less than 30 which are regarded as an effective additive in the prior arts, and that the carbon atom numbers are specified based on a balance between the heat resistance and the suppression of BS because the investigations of the prior arts did not cover these molecular weight distribution.
In the present invention, the aforementioned problems could be solved by specifying the ranges or the molecular weight distributions and purities of the aliphatic higher alcohols or the higher fatty acids, said molecular weight distributions and purities being not investigated in the prior arts.
According to the present invention, it is possible to suppress BS and to achieve a sufficient heat resistance by adding dramatically small amounts of the higher alcohols or higher fatty acids to the toner. In addition, it is possible to minimize an influence on the other properties of the toner because a sufficient suppression of BS can be achieved by adding not more than 1 part by weight of the higher alcohols or higher fatty acids to 100 parts by weight of toner particles.
The functions of the present invention will be explained hereinafter.
It is possible to insure the starting temperature of the melting of at least 55xc2x0 C. because the aliphatic higher alcohols or higher fatty acids used in the present invention hardly contain the low-molecular ingredients whose carbon atom numbers are not more than 20, and there is little influence thereof on the maintenance of -heat resistance of the toner.
Furthermore, it is thinkable that a formability of a lubricating film at the time of blade cleaning becomes favorable without being too hard, and a surface energy of the photosensitive member is lowered to make an adhesion of the components of the toner difficult because the aliphatic higher alcohols or higher fatty acids used in the present invention hardly contain the high-molecular ingredients whose carbon atom numbers are not less than 30.
Namely, as the heat resistance and the formability of lubricating film on the photosensitive member of the toner are contrary properties, the best range of carbon atom numbers of the aliphatic higher alcohols or higher fatty acids is an range of 21-29 for a compatibility of the both properties. In addition, the object of the present invention can also be achieved provided that a distribution of the ingredients whose carbon atom numbers are not more than 20 is not more than 2% and that a distribution of the ingredients whose carbon atom numbers are not less than 30 is not more than 2%.
The toner according to the present invention contains (i) toner particles comprising at least a binding resin and a colorant and (ii) the aliphatic higher alcohols and/or higher fatty acids which are externally added to the toner particles, and a releasant and a charge-controlling agent are suitably added to the toner particles as occasion demands. Furthermore, post-treating agents, such as a fluidizing agent and the like are externally added to the toner particles as occasion requires.
The publicly known binder resins may be employed as the binder resin in the present invention. For example, the following resins are suitably employed: styrene resins, acrylic resins (e.g., alkyl acrylate resin, alkyl methacrylate resin and the like), styrene-acrylate copolymerization resins, polyester resins, silicone resins, olefin resins, amido resins, epoxy resins and the like.
In order to increase a light permeability of OHP and a color reproducibility of the superposed image, high transparency, low melting viscosity and high sharp melt property are required for the binding resin for a full color toner. Polyester resins are suitable for the binding resin having these properties.
As the full color toner contains the binder resin having the aforesaid properties, it is necessary to externally add many post-treating agents to the toner particles in order to increase a fluidity and a blocking tendency.
With respect to the binder resin used for full color toners such as cyan toner, magenta toner and yellow toner in the present invention, those resins having the following properties are preferably used: a number-average molecular weight (Mn) of 3000 to 6000, preferably 3500 to 5500, a ratio Mw/Mn of weight-average molecular weight (Mw) to number-average molecular weight (Mn) of 2 to 6, preferably 2.5 to 5.5, a glass transition point of 50 to 70xc2x0 C., preferably 55 to 70xc2x0 C., and a softening point of 90 to 110xc2x0 C., preferably 90 to 105xc2x0 C.
The number-average molecular weight less than 3000 of the binder resin tends to cause image defects (degradation in fixing properties at the time the sheet is bent) due to separation of image portions when a full-color solid image is bent. The number-average molecular weight exceeding 6000 causes deterioration in the thermal fusing properties with the result that the fixing strength is lowered. The value of Mw/Mn smaller than 2 tends to cause high-temperature offset. The value exceeding 6 tends to cause deterioration in the sharp melting properties at the time of fixing, resulting in deterioration in the toner light-transmitting properties and the color-mixing properties at the time of a full-color image-formation. The glass transition point lower than 50xc2x0 C. makes the heat resistant properties of the toner insufficient, making the toner susceptible to aggregation at the time of storing. The glass transition point higher than 75xc2x0 C. causes deterioration in the fixing properties as well as deterioration in the color-mixing properties at the time of a full-color image formation. The softening point lower than 90xc2x0 C. tends to cause high-temperature offset, and the value exceeding 110xc2x0 C. tends to cause deterioration in the fixing strength, the light-transmitting properties, the color-mixing properties and the gloss properties in full-color images.
The publicly known pigments and dyes may be adopted as a colorant. Examples thereof include carbon black, aniline blue, Chalco Oil Blue, chrome yellow, ultramarine blue, DuPont Oil Red, quinoline yellow, methylene blue chloride, copper phthalocyanine, Malachite green oxalate, Lump Black, Rose Bengal. As a colorant for the magenta toner, C.I. Pigment Red 48:1, C.I. Pigment Red 122, C.I. Pigment Red 57:1 and C.I. Pigment Red 184 may be employed. As a colorant for yellow toner, C.I. Pigment Yellow 97, C.I. Pigment Yellow 12, C.I. Pigment Yellow 180, C.I. Pigment Yellow 17, C.I. Pigment Yellow 93 and C.I. Solvent Yellow 162 may be employed. As the colorant for the cyan toner, C.I. Pigment Blue 15:1 and C. I. Pigment Blue 15:3 may be employed. When the toner of the present invention is used as a magnetic toner, some or all amount of the colorant may be replaced by a magnetic material. Examples of such a magnetic material include magnetite, ferrite, iron power, nickel powder, etc.
From the viewpoints of an afforability of fluidity, an increase of cleanability and the like of the toner according to the present invention, post-treating agents may be added to and mixed with the toner particles. Although the post-treating agents are not particularly restricted, the following additives may be employed: inorganic oxide fine particles (e.g., silica fine particles, alumina fine particles, titanium fine particles and the like), fine particles of metallic salts of stearic acid (e.g., aluminum stearate fine particles, zinc stearate fine particles and the like) and inorganic titanate fine particles (e.g., strontium titanate fine particles, zinc titanate fine particle and the like). These additives can be used independently or jointly. From the viewpoints of the environmental stability and the maintenance of heat resistance, it is desirable to use these fine particles after their surfaces are treated with a silane coupling agent, a titanium coupling agent, a higher fatty acid, a silicone oil and the like. An adding amount of these fine particles is 0.05-5 parts by weight, preferably 0.1-3 parts by weight relative to 100 parts by weight of the toner particles.
In order to increase the anti-offset properties, etc., the toner of the present invention may contain a wax as a releasant. Examples of such a wax include polyethylene wax, polypropylene wax, carnauba wax, rice wax, sazol wax, montan ester waxes, Fischer-Tropsch wax, etc. In the case of addition of a wax to the toner, the content is preferably in the range of 0.5 to 5 parts by weight relative to 100 parts by weight of the binder resin. Thereby, it becomes possible to obtain the effects of the addition without causing disadvantages, such as filming, etc.
From the viewpoint of improvement in anti-offset properties, polypropylene wax is preferably contained. From the viewpoint of improvements in smear-preventive properties (xe2x80x9csmearxe2x80x9d means a phenomenon in which, when a paper-sheet with images copied on its one side is fed by an automatic document-feeding apparatus or in a double-sided copying machine, degradation in the copied image, such as blurring and stains, occurs due to friction between the sheets or between the sheet and rollers on the image), polyethylene wax is preferably contained. From the above-mentioned viewpoints, the polypropylene wax is preferably set to have a melt viscosity of 50 to 300 cps at 160xc2x0 C., a softening point of 130 to 160xc2x0 C. and an acid value of 1 to 20 KOH mg/g. The polyethylene wax is more preferably set to have a melt viscosity of 1,000 to 8,000 cps at 160xc2x0 C. and a softening point of 130 to 150xc2x0 C. The polypropylene wax having the above-mentioned melt viscosity, softening point and acid value exhibits a superior dispersing properties to the binder resin. The anti-offset properties are improved without causing problems due to isolated wax. In addition, the polyethylene wax having the above-mentioned melt viscosity, softening point and acid value also exhibits a superior dispersing properties to the binder resin. The polyethylene wax can increase the smear-preventive properties by decreasing a friction coefficient of the fixed image surface without causing problem due to isolated wax. Further, the melt viscosities of the waxes were measured by means of Brookfield type viscometer.
As a charge-control agent for a positive charge-toner, the following positive charge-control agents are exemplified: Nigrosine Base EX of azine compounds, Bontron N-01, Bontron N-02, Bontron N-04, Bontron N-05, Bontron N-07, Bontron N-09, Bontron N-10, Bontron N-13 (Orient Kagaku Kogyo Co.); Oil Black (Chuou Gosei Kagaku Co.); quaternary ammonium salt P-51, polyamine compound P-52, Sudan Chief Schwartz BB (Solvent Black 3: C.I. No. 26150), Fett Schwartz HBN (C.I. No. 26150), Brilliant Spirit Schwartz TN (Farbenfabriken Bayer Co.); alkoxylated amine, alkyl amide, molybdenum acid chelate pigments, imidazole compounds and the like.
As a charge-control agent for a negative charge-toner, the following negative charge-control agents are exemplified: chrome complex type azo dyes S-32, S-33, S-34, S-35, S-37, S-38, S-40 (Orient Kagaku Kogyo Co.); Aizen Spilon Black TRH, Aizen Spilon Black BHH (Hodogaya Kagaku Co.); Kayaset Black T-22, Kayaset Black 004 (Nihon Kagaku Co.); Copper phthalocyanine dye S-39 (Orient Kagaku Kogyo Co.); chrome complexes E-81, E-82 (Orient Kagaku Kogyo Co.); zinc complex E-84 (Orient Kagaku Kogyo Co.); aluminum complex E-86 (Orient Kagaku Kogyo Co.); calix arene compounds and the like.
With respect to the negative charge-control agent used for full color toners, colorless, white or light-colored charge-control agents, which do not give adverse effects on the tone and the light-transmitting properties of the color toner, may be applied. Examples thereof include metal complexes of zinc and chromium of salicylic acid derivatives, calix arene compounds, organic boron compounds, quaternary ammonium salt compounds containing fluoride, etc. With respect to the metal complex of salicylic acid derivative, for example, those disclosed in U.S. Pat. No. 4,206,064, U.S. Pat. No. 4,762,763 etc. may be adopted. With respect to calix arene compounds, for example, those disclosed in U.S. Pat. No. 5,049,467, etc. may be adopted. With respect to organic boron compounds, for example, those disclosed in U.S. Pat. No. 5,863,692, etc. may be adopted. With respect to quaternary ammonium salt compounds containing fluoride, for example, those disclosed in U.S. Pat. No. 5,069,994, etc. may be adopted.
With respect to the aliphatic higher alcohols or higher fatty acids which are externally added to the surfaces of the toner particles, the number-average carbon atom numbers of said alcohols or fatty acids are 21-29, and the weight percentage of the ingredients whose carbon atom numbers are not more than 20 and the weight percentage of ingredients whose carbon atom numbers are not less than 30 are both not more than 2%. The aforesaid higher alcohols or higher fatty acids may be a single ingredient or a mixture thereof.
In the case where the number-average carbon atom numbers are not more than 20 or where the weight percentage of the ingredients whose carbon atom numbers are not more than 20 is not less than 2% even if the number-average carbon atom numbers are not less than 21, the starting temperature of melting becomes lower than 52xc2x0 C., and the heat resistance of the toner when said alcohols or fatty acids are added to the surfaces of the toner particles becomes worse. Therefore these embodiments are not preferable.
On the other hand, in the case where the number-average carbon atom numbers are not less than 30 or where the weight percentage of the ingredients whose carbon atom numbers are not less than 30 is not less than 2% even if the number-average carbon atom numbers are not more than 29, their lubricative film-forming properties on the photosensitive member becomes worse and their BS suppressing effects are decreased because their melting points become higher to increase their hardness. Therefore these embodiments are also unpreferable.
Preferable average particle sizes of the aliphatic higher alcohols or higher fatty acids employed in the present invention are 2-10 xcexcm, more preferably 4-8 xcexcm. It is suitable to employ the higher alcohols or higher fatty acids from which the ingredients having finer particle sizes are removed. When said average particle sizes are less than 2 xcexcm, the charging property and heat resistance of the toner become worse and the problems such as the filming to the photosensitive member and the like may occur. Therefore this embodiment is not preferable. On the other hand, when the average particle sizes are more than 10 xcexcm, the lubricative film-forming effect on the photosensitive member becomes weak and the problem may occur wherein a blank will appear around the coarse particles at the time of transferring the toner. Therefore this embodiment is also unpreferable.
Although an adjusting method of the particle sizes is not particularly restricted, a dry process wherein a solid block of the aforesaid alcohols or fatty acids is ground in a dry state and the ground powders are classified or a wet process wherein said alcohols or fatty acids are emulsified in a liquid and the emulsion is subjected to a drying treatment can be employed.
With respect to an adding amount of aliphatic alcohols or fatty acids, it is preferable to use 0.05-3 parts by weight, more preferably 0.1-1 part by weight relative to 100 parts by weight of the toner particles. When the adding amount is less than 0.05 part by weight, BS suppressing effect is remarkably decreased. On the other hand, when the adding amount is more than 3 parts by weight, an electrification amount of the toner is decreased and a fogging of an image will occur. Therefore both embodiments are unpreferable.
With respect to a process for preparing the toner of the present invention, any of the publicly known preparation methods can be employed. For example, dry processes, such as grinding method and the like, and wet processes, such as an emulsion polymerization method, a suspension polymerization, an emulsion granulation method and the like can be mentioned. Generally speaking, the grinding method provides the particles having an indefinite shape, and the wet processes provide spherical particles. The preparation methods of the toner which is suitable for an image formation process may be employed. From the viewpoint of an image quality, a toner having a small particle size is preferably employed, and the loners having volume-average particle sizes of about 4-10 xcexcm can suitably be used. In particular, the object of the present invention relating to the toner can be achieved by adopting any of the preparation methods and particle sizes.
With respect to a process for externally adding the aliphatic higher alcohols or higher fatty acids used in the present invention to the toner particles as an external additive, a general process is as follows: said alcohols or fatty acids are mixed with the toner matrix particles together with the post-treating agents (e.g., a fluidity-affording agent, an improver of cleanability and the like), and then the mixture is treated by means of Henschel mixer. However the process for adding said external additive is not restricted to the general process.
As regards a composition of the developer, although magnetic one-component developer, non-magnetic one-component developer, magnetic two-component developer and non-magnetic two-component developer may generally be used, the object of the present invention relating to the toner can be achieved by employing any of these developers.